1. Field of the Invention
This invention is in the field of fuel injection systems for internal combustion engines, and particularly fuel injection system for four stroke cycle engines which inject the fuel into the engine intake manifold.
2. Description of the Prior Art
Within the past several years the gasoline engine carburetor has been largely replaced with intake manifold gasoline injector systems in many engine applications. Most of these prior art gasoline injector systems inject the fuel at constant pressure and control the fuel quantity by controlling the time duration of injection. An electronic controller, responsive to engine intake air flow rate and engine speed sensors, adjusts times duration of fuel injection so as to maintain the desired overall air to fuel ratio created in the intake manifold. The electronic controller can be additionally responsive to engine exhaust gas composition sensors which provide a feedback control to more closely adjust fuel injection duration, and hence overall air to fuel ratio, for minimum emission of undesirable exhaust gas constituents. This capability of using a feedback control from the exhaust is a principal reason why carburetor fuel systems were replaced with fuel injector systems, since it is difficult to properly introduce feedback control into a carburetor system.
A particular benefit of typical carburetor fuel systems is that the instantaneous rate of fuel flow is roughly proportional to the instantaneous rate of air flow. As a result, during each engine intake stroke, regions of excessively lean air to fuel ratio and other regions of excessively rich air to fuel ratio can be largely avoided and a roughly uniform instantaneous air to fuel ratio is created in each intake mixture charge going into each engine cylinder.
Present gasoline injector systems tend to create both excessively rich air fuel mixture regions and excessively lean air fuel mixture regions since the instantaneous rate of fuel flow is not proportioned to the instantaneous rate of air flow into the engine intake manifold. While fuel injection is taking place an over rich region is created, and, after injection ceases an over lean region is created during each engine intake stroke. The over rich region and the over lean region survive compression, in large part, and their subsequent combustion creates undesirable emission components characteristic of both over lean operation and over rich operation even though the overall air fuel ratio is neither over rich nor over lean.
A principal undesirable exhaust emission from over lean mixtures is oxides of nitrogen, whereas from over rich mixtures carbon monoxide and unburned hydrocarbons are among the undesirable exhaust emissions. Between these over lean mixtures and over rich mixtures a rather narrow "window" of mixture ratios exists where net emissions of both types of undesirable exhaust constituents can be minimized. Yet, even when the overall mixture ratio of an engine lies within this narrow "window," excess emissions may occur if this overall mixture is non uniform and stratified, as when present gasoline injector systems are used which create both over lean regions and over rich regions within each air fuel mixture charge going into each engine cylinder.
It would be very beneficial to have available a gasoline fuel injection system, capable of proportioning instantaneous fuel flow rate to instantaneous air flow rate so that a uniform mixture ratio existed, and lying within the minimum net emissions window, for each air fuel mixture charge going into each engine cylinder over a wide range of engine operating conditions. Yet further reductions of undesirable exhaust emissions could be achieved in this way.
3. Definitions
The devices of this invention are intended to be used with a four stroke cycle internal combustion engine mechanism, comprising various elements as are well known in the prior art of internal combustion engines, of which the following elements connect to or cooperate with the devices of this invention:
A. Pistons operate within cylinders, and are driven from a rotating crankshaft, via a connecting rod, to vary the volume of a variable volume chamber enclosed between the cylinder walls and the piston crown. PA1 B. Intake valves, at least one for each cylinder, connect and disconnect the variable volume chamber to and from an intake air supply manifold. PA1 C. Exhaust valves, at least one for each cylinder, connect and disconnect the variable volume chamber to and from an exhaust gas manifold. PA1 D. These intake and exhaust valves are opened and closed by a valve drive means driven in turn from the engine crankshaft so that each engine cylinder carries out a four stroke cycle which is repeated. This four stroke cycle comprises, in time order: an air intake stroke whenever the piston is moving to increase the volume of the variable volume chamber and the intake valve is open and the exhaust valve is closed; a compression stroke whenever the piston is moving to decrease the volume of the variable volume chamber and both intake and exhaust valves are closed; an expansion stroke whenever the piston is moving to increase the volume of the variable volume chamber and both intake and exhaust valves are closed; an exhaust stroke whenever the piston is moving to decrease the volume of the variable volume chamber and the exhaust valve is open and the intake valve is closed. PA1 E. A fuel supply source supplies fuel to the engine and this fuel is mixed into the intake air in the intake manifold. PA1 F. An ignition means ignites the air fuel mixture at some time during the latter part of the compression stroke or the early part of the expansion stroke, and a combustion process thus intervenes between compression and expansion processes. Electric spark ignition means are commonly used but compression alone can be used to cause compression ignition of the air fuel mixture. PA1 G. In many engine applications a torque control means is used for controlling the torque output via the engine crankshaft averaged during at least one or more of the four stroke cycles. For gasoline fueled internal combustion engines the torque controller is often a throttle valve in the air intake manifold which, by controlling the air density during the intake stroke, controls the mass air flow rate per intake stroke, and thus the air mass quantity available for combustion and thus controls the torque output. An intake air supercharger can be used additionally or alternatively as a means for controlling the air density during the intake stroke. For diesel fueled internal combustion engines, using compression ignition, the torque controller usually functions to control the fuel mass flow rate per intake stroke, and thus the fuel quantity available for combustion. PA1 H. During each intake stroke the instantaneous air mass flow rate varies greatly, being related to the velocity of motion of the piston during intake. Since piston velocity changes from zero at the start and end of the intake stroke to maximum during the middle portion of the intake stroke, instantaneous air mass flow rate correspondingly varies from zero or low at the start and end of the intake stroke to maximum during the middle portion of the intake stroke. PA1 I. The instantaneous fuel mass flow rate is not necessarily related to the piston velocity or the instantaneous air mass flow rate but depends upon the fuel introduction device used. When a carburetor is used to introduce fuel into the air intake manifold it is the instantaneous air flow rate through the carburetor venturi which generates the pressure difference forcing fuel into the intake manifold. As a result a rough correspondence exists between instantaneous air flow rate and instantaneous fuel flow rate when a carburetor is used. When a timed fuel injector is used, at constant fuel nozzle pressure difference, the instantaneous fuel flow rate is essentially constant during injection, the total fuel quantity injected per intake stroke being proportioned to the total air quantity per intake stroke by controlling the duration of fuel injection. PA1 J. The mean value of air fuel ratio during any one engine intake stroke is the mass ratio of the air flow rate per intake stroke to the fuel flow rate per intake stroke. If electric spark ignition is used to initiate the combustion process this mean value of air fuel ratio must be kept within the spark ignition range. Where compression ignition is used to initiate the combustion process this mean value of air fuel ratio can be varied over a wider range than the spark ignition range.